Fair Value Fair Value of Derivative Contracts (Details) (USD $)	3 Months Ended		6 Months Ended																					6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	May 01, 2013	Jun. 30, 2013 Estimate of Fair Value [Member] Commodity Contract [Member]	Dec. 31, 2012 Estimate of Fair Value [Member] Commodity Contract [Member]	Jun. 30, 2013 Estimate of Fair Value [Member] Interest Rate Swap [Member]	Dec. 31, 2012 Estimate of Fair Value [Member] Interest Rate Swap [Member]	Jun. 30, 2013 Quoted prices in active markets for identical assets (Level 1) [Member] Commodity Contract [Member]	Dec. 31, 2012 Quoted prices in active markets for identical assets (Level 1) [Member] Commodity Contract [Member]	Jun. 30, 2013 Quoted prices in active markets for identical assets (Level 1) [Member] Interest Rate Swap [Member]	Dec. 31, 2012 Quoted prices in active markets for identical assets (Level 1) [Member] Interest Rate Swap [Member]	Jun. 30, 2013 Significant other observable inputs (Level 2) [Member] Commodity Contract [Member]	Dec. 31, 2012 Significant other observable inputs (Level 2) [Member] Commodity Contract [Member]	Jun. 30, 2013 Significant other observable inputs (Level 2) [Member] Interest Rate Swap [Member]	Dec. 31, 2012 Significant other observable inputs (Level 2) [Member] Interest Rate Swap [Member]	Jun. 30, 2013 Significantunobservable inputs (Level 3) [Member] Commodity Contract [Member]	Dec. 31, 2012 Significantunobservable inputs (Level 3) [Member] Commodity Contract [Member]	Jun. 30, 2013 Significantunobservable inputs (Level 3) [Member] Interest Rate Swap [Member]	Dec. 31, 2012 Significantunobservable inputs (Level 3) [Member] Interest Rate Swap [Member]	Jun. 30, 2012 Minimum [Member]	Jun. 30, 2012 Maximum [Member]	Jun. 30, 2013 El Paso Corporation [Member]	Jun. 30, 2012 El Paso Corporation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets						$ 159,000,000	$ 107,000,000	$ 310,000,000	$ 665,000,000	$ 14,000,000	$ 3,000,000	$ 0	$ 0	$ 89,000,000	$ 76,000,000	$ 310,000,000	$ 665,000,000	$ 56,000,000	$ 28,000,000	$ 0	$ 0
Fair Value, Assets Liabilites Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning of Period	(142,000,000)	(3,000,000)	(155,000,000)	7,000,000	(114,000,000)
Total gains (losses), Included in earnings	(6,000,000)	(3,000,000)	(1,000,000)	(1,000,000)
Total gains (losses), Included in other comprehensive income	1,000,000	28,000,000	0	6,000,000
Purchases	18,000,000	(246,000,000)	18,000,000	(243,000,000)																				18,000,000	246,000,000
Settlements	15,000,000	4,000,000	24,000,000	11,000,000
End of Period	(114,000,000)	(220,000,000)	(114,000,000)	(220,000,000)	(114,000,000)
The amount of total gains or (losses) for the period included in earnings attributable to the change in unrealized gains or (losses) relating to assets held at the reporting date	1,000,000	(4,000,000)	4,000,000	(3,000,000)
Derivative Financial Instruments, Liabilities, Fair Value Disclosure						(192,000,000)	(212,000,000)	(49,000,000)	(1,000,000)	(4,000,000)	(3,000,000)	0	0	(18,000,000)	(26,000,000)	(49,000,000)	(1,000,000)	(170,000,000)	(183,000,000)	0	0
Price of Mega Watts Per Hour																						$ 24.14	$ 57.13